Hydrodynamic gear transmission



l.. A. TROFIMOV HYDRODYNAMIC GEAR TRANSMISSION June 2, 1953 2 Sheets-Sheet l Filed March 11, 1949 f/ a/llll/ m.

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v HYDRODYNAMIC GEAR TRANSMISSION Filed March 1l, 1949 2 Sheets-Sheet 2 M wss I N Q b \s '91l l m q, l 0 2 C? m Q a @o a .i q\\ l\ 1) m Q m M INVENTOR.A

ev H. Wolf/'mov BUG/WWW Patented June 2, 1953 UNITED STATES iTENT OFFICE HYDRODYNAll/HC GEAR TRANSMISSION Lev A. Trohmov, Willoughby, Ohio Application March 11, 1949, Serial No. 80,871

This invention relates to power transmissions and particularly to power transmissions for transmitting to a load, the power of' a motor which runs continuously at full speed or at high-power emcient speed;` the control of the transmitted speed being eilected by control of the transmission as distinguished from control of the motor.

The invention is adaptable to drive loads which are to be started and driven at constant speed, orl at variable speed, in one direction; or in either the forward or the reverse direction, and brought to rest from either direction; and to loads of either the overhauling or the non-overhauling type; and to loads that are to be started and moved to a desired position and brought to rest in that position; and to moving loads that are to be quickly braked to stop them.

In one form, the transmission of the invention comprises in general, a power output element or shaft; differential gearing driven by the continuously running motor; and hydrodynamic means developing torque upon which the gearing reacts, and which is variable by a control; and the output element is driven in one direction and at speeds corresponding to the amount of developed torque.

In the preferred form, the invention comprises a double diierential gearing, and a pair of hy- 6- Claims. (Cl. 745-750) drodynamic means developing two turques upon which the gearing reacts; and which, when the torques are equal or balanced, holds the output element at rest; and when unbalanced, or one or the other predominates, causes the output shaft to rotate in one direction or the other accordingly, and at speed commensurable with the degree of imbalance.

A part of the invention resides in the improved means for developing hydrodynamic torque for the purposes mentioned.

The objects of the invention are therefore:

To provide a power transmission having all or at least som@ of the foregoing features and modes of operation;

To provide in a transmission of the type referred to improved hydrodynamic variable torque developing means, and controls therfor.

The invention is fully disclosed in the following description take-n connection with the accomu panying drawing, in which:

Fig. 1 is a view, in some respects diagrammatic, showing an apparatus embodying the invention in one form, the apparatus being partly in longitudinal section;

Fig. 2 is a fragmentary Vcross sectional view from the piane 2--2 of Fig. 1;

Fig. 3 is a view similar to Fig. 2 but from the plane 3-3 of Fig. 1;

Fig. 4 is a View similar to Fig. 1 but illust-rating a modification.

Referring to the drawings Figs, 1, 2, and 3, which as mentioned are in somewhat diagrammatic form, there is shown an embodiment of the invention in which a double differential gearing is utilized comprising a dierential gearing I and a diierential gearing 2.

The gearing l comprises a carrier or spider ele-i ment 3i, rotatably supporting a pinion or pinions i meshing with differential gears 5 and 6.

The gearing 2 comprises similarly a carrier or spider element T rotatably supporting a pinion or pinions 6--8 meshing with dierential gears 9 and lo.

In this embodiment of the invention, it is contemplated that the spider elements 3 and l are to rotate in opposite directions and at equal speeds and to this end are of equal diameter and are provided with gear teeth on the outer peripheries mashed with each other at Il; and it is contemplated that the motor power input fis to be at the spider elements 3 and l; and accordingly a continuously running power supply motor i2 drives a gear i3 meshed with one of the spider elements, for example, the spider element 3.

Connected to the dilerential gears 5 and 9 respectively are gears or pinons lil5, meshed with a gear It to which is connected the power output element il, which in this embodiment is a rotary output shaft.

The diiierential gear 5 is connected to a tubular shaft I8, and the spider element 3 is connected to a shaft I9 coaxial within the tubular shaft I8, and the shafts l 8 and i9 are connected to a hydrodynamic torque developing unit shown generally at 20. v

The differential gear lil and the spider element l are similarly connected to a hydrodynamic torque developing unit 23 by a tubular shaft 2l and coaxial shaft 22.

Bearings for the gears and shafts above referred to have been omitted in the diagrammatic showing for simplicity, but the same will be understood by those skilled in the art.

The units E8 and 23 will presently oe described, but at this point it is to be noted that with the power driven differential gearing thus far clescribed, and with the spiders 3 and 1 driven in opposite directions, the gears ii and it will tend to rotate in opposite directions and if braking or restraining torques were developed on the shafts i8 and 2i, they would be in opposite directions and this would cause torques to be developed in opposite directions at the dierential gears and 9, and at the gears I4 and I5.

Also, if there is little or no braking or restraining torque on the shafts I8 and 2 I, they will tend to be driven at equal speeds and at twice the speed of their associated spiders 3 and 1, and there will ybe little or no torque at the gears 5--I4 and 9-I5, and the gear I5 and output shaft I1 will remain at rest; but if braking or restraining torque is developed on the shaft 2l, or if more torque is developed on the shaft 2| than on the shaft I8, more input torque will be required from the spider 1 to drive the gear IB than from the spider 3 to drive the gear 5, and the gear I5 and its shaft 2l will slow down, and the gear 6 and its shaft I8 will speed up, and more torque will be developed at the gears 9 and I5 than at the gears 5 and I4; and the gear I5 will rotate the gear I6 and output shaft I1 in a corresponding direction; and the gear I will rotate the gears I4 and 5, and this will cause gea-r 6 to speed up, as stated, and speed up its shaft I8.

As a matter of fact, in the gearing arrangement illustrated, the arithmetical sum of the speeds of the shafts 2I and I8 is always a constant.

If braking or restraining torque were developed on the shaft I8 (instead of on the shaft 2| as described) then the output shaft I1 would be driven in the opposite direction, as is believed will now be clear.

Thus, by developing braking or restraining torques on the shafts I8 and 2l, and controlling them to make them equal 4or to make one predominate over the other the output shaft I 1 may be held at rest, or may be driven in either the forward or reverse direction, and in each `case at a speed commensurable with the degree to which one torque predominates over the other.

Braking or restraining torque as referred to is developed by the hydrodynamic units 2li- 23, by developing braking or restraining action on the shafts I8 and 2I. These units may be alike and a description of one of them, the unit 20, for example, will suce.

On the end of the shaft I8 is a coaxial cupshaped housing 24, having a transverse bottom wall 25, a tubular side wall 26, and slots or radially open keyways 21 in the side Wall, four being shown in Figs. 2 and 3.

The shaft I9 extends through the `bottom 25 and coaxially through and beyond the tubular wall 25; and has longitudinal keyways 28-28 four being shown in Figs. 2 and 3.

A set of discs 29-29 having central openings Sli- 38, and a set of discs 3'I-3I having central openings 32-32, are telescoped by their openings over the shaft I9, discs of one set alternating with discs of the other set, and constituting a tier of discs.

The discs 29-29 have clearance at their central openings with the shaft I9. At their peripheries, they have clearance with the tubular Wall 26 and are supported therein and keyed to rotate therewith by peripheral keys or tongues 33-33 extending into the keyways 21; whereby the discs 29 may oat axially and without rotating within the housing wall 2B.

The discs 3I-3I are telescoped on the shaft I9 by their central openings 32-32 and have keys or tongues 34-34 extending into the keyways 28-28 of the shaft, and having clearance therewith; whereby the discs 3I--3I may oat axially on the shaft and rotate therewith.

The shaft I9 has an axially extending oil duct 35 extending from its outer end to or beyond the innermost disc '29; and at its outer end projects into a housing 36 in which it rotates and to which it is Isealed by packing rings 31-31; and a pump 38 driven by a motor 39 draws oil from a reservoir 48 by an intake pipe 4I and lsupplies it by a pipe 42 to the housing 3B and thence to the shaft duct 35.

The shaft I9 has a plurality of radialbranch ducts 43 from the axial duct 35 and these discharge the supplied oil into the said central opening clearance spaces between the shaft and the discs; whence it ows radially outwardly between the discs to the housing wall 26 and out at the radially open keyways 21 and thence falls into the reservoir 48.

The reservoir 40 may conveniently be a housing having an enclosing wall 44 for the units I and 2 as plainly shown in Fig. 1, the shafts I8-I9 and 2I-22 extending through the wall 44 at suitable openings 45--46.

In the arrangement of discs illustrated, one of the discs 29 lies against the housing bottom 25 and one of the discs 3l is at the other or inner end of the tier of discs.

Spaced axially from the tier of discs is a thrust bearing plate 41, rotatable on bearing balls 48 upon one spool head 49 of a spool 58 surrounding the shaft I9 with clearance, and having anlother spool head 5I.

Between the spool heads 49 and 5I is one end 52 of a rocking lever 53', having a pivot bearing 54 at an intermediate point, upon a post 55.

Between and abutting at its ends upon the bearing plate 41 and upon the innermost disc 3| is a spring 56 surrounding the shaft I9.

When the lever 53 is rocked clockwise on its pivot bearing 54, as viewed in Fig. 1, movement of the lever is communicated through the spring to the tier of discs 3I-29 to move them closer together; the spring 56 ybeing free to rotate with the disc 3l upon which it abut's, by the bearing 41-48,

As stated, the lunit 23 may be, and preferably is, like the unit 2G above described, having an enlargement 52A on the lever 53 in a spool 50 for the same purposes as the en-d 52 of the lever.

The position of the pivot bearing 54 is made adjustable `by providing the bearing post 55 with a threaded stud 51 extending through a plain bore in a post 58 and having nuts 59-60 on opposite sides of the post. By unscrewing one nut and screwing up the other, the position of the pivot bearing 54 may be adjusted.

The oil circulated as described by the pump 38, supplies and maintains oil lms between the pairs of adjacent discs, as described, the films being made thinner in the unit 2U and thicker in the unit 23 when the lever 53 is rocked clockwise as viewed in Fig. l, and vice versa when rocked counterclockwise. The pressure of the oil supplied to the discs at their centers and flowing voutwardly over the discs as they rotate tends to separate the discs whereby the thickness of the films always corresponds to the rocked position of the lever 53.

These oils lms as will be more fully described are not for merely lubricating the discs, but are thicker than lubricating films, and transmit torque hydrodynamically from one set of discs 29--29 to the other set 3I--3I.

It is to be noted that the springs 56 are not normally under compression and do not normally exert resilient compressive force on the the output shaft the screw 64 is rotated back to a neutral position by the hand wheel 65. The load can thus be driven in the forward or reverse direction and at a desired speed in either direction by rotation of the hand wheel 65.

During this hand control, the shaft 15 and hand wheel 16 will be rotated idly through the differential gearing 61, by rotation of the hand wheel 65 or by rotation of the load shaft I1 or both.

Again, if the load on the output shaft I1 is one which it is desired to drive accurately at a constant preselected speed, then the clutch 11-19 would be engaged by the lever 18 and the hand wheel B4 would be turned, to set the transmission 82 to drive its output shaft 15 at a set constant speed. It may be assumed for simplicity that at the time when the clutch 11--19 is engaged, the output shaft is at rest.

The transmission 82 now rotates the shaft 15, gears 14-13, and dilerential gear 10, the latter at a set speed. The other differential gear 69 is at rest and the gear 'I6 acting through the pinions 68-68 turns the spider 66 and the screw 64, thereby rocking the lever 53 to cause the output shaft I1 to turn. Rotation of the latter, acting through the gear 12 and shaft 1I turns the differential gear 69 in the direction opposite to the direction of the differential gear and the increasing speed of the gear 69 brings it up to a speed equal to that of the differential gear 10- and thereupon the spider 66 stops rotating and stops rocking of the lever 53, and the output Shaft I1 thereafter rotates at the speed which it has by this time attained.

If the output shaft I1 should, because of an increase of load thereon, tend to slow down, this will slow down rotation of the gear 69 and the gear 10 still rotating at its constant set speed will rotate the spider 66 and cause further rocking yof the lever 53 to increase the speed of the load shaft and restore it to its preselected speed again. Any tendency of the load shaft to increase in speed is corrected by a similar response in the reverse sense when the gear 69 begins to rotate faster than the gear 10.

The speed of the output shaft can thus be set at a constant speed at any time by rotation of the hand wheel 34 to a corresponding position; and the control will automatically maintain that load speed.

During this control and automatic regulation of speed, the hand wheel 16 will rotate idly continuously; and the hand wheel 65 will rotate idly fromtime to time as regulating action goes on. The motor driven transmission 8l may be of very small fractional horsepower, incapable'itself of driving the load on the shaft I1, wherebyV the motor I2 and output shaft I1 and associated elements of the main differential gearing transmission may be of large size able to transmit very great horsepower, the unit 8| being a speed reference unit having only power enough to operate the screw 64.

' Again, the output shaft I1-may be connected to a load which is to be moved to adesired position and left in that position. Illustrative of such uses is the positioning of airport wind direction signals or the aiming of guns by motor power. In such a case, the output shaft I1 is to be rotatedfpreferably at high speed for a number of revolutions and .then automatically slowed down and stopped. To effect this control the clutch 11.-19 is disconnected and the hand wheel 16 is turned. This turns the differential gear 1D and through the pinions 68 turns the spider 66, and

the screw 64 turns and this. causes the shaft I1 to start and accelerate.

Rotation of the output shaft I1 turns differential gear 69 in the direction to neutralize thej effect on the spider 6G of rotation of the differential gear 16. Thus so to speak the differential gear 69 tries to catch up with the differential gear 1B. The faster the wheel 16 is turned the more will the speed of differential gear 1I] stay ahead of the speed of differential gear 69 and keep the screw 64 turning and keep the lever 53 rocked more and more from its neutral position. There is a speed of rotation for the hand wheel 1'5 at which the screw 64 will nally become stationary and cause the output shaft I1 to have a corresponding speed. Ii' rotation of the wheel 16 is slowed -down below that speed or is stopped altogether, then the speed of ,the differential gear 69 will catch up with and pass beyond that of the differential gear 10, and turn the screw 64 in the other direction, causing the output shaft I1 to slow down and when the lever 53 has in this manner been brought to its neutral positions, the load shaft I1- will stop.

During this control, the hand wheel 65 rotates idly.

In the case of control by the hand wheels 65 'or 16 as described, the load whether it is an overhauling load, as when the load shaft I1 drives a hoist cable drum, orA whether it is one moving with inertia, improved dynamicbraking may be had by the transmission. I

Heretofore dynamic braking has been effected by causing the power input motor itself to act as an electric generator driven by the load. Such prior dynamic braking is highly effective (although requiring complications of electric circuits and contacts to control them) but only at high speeds of the load. As the load is slowed down, the generator is driven more slowly and generates decreasing electric power and decreasing brake torque; and is therefore less effective at low load speeds and become wholly ineffective as the load approaches zero speed, and to stop and hold the load, a supplemental friction brake has had to be added. In the present invention, to quickly brake and stop an overhauling load or an inertia load, the screw 64 may be rotated to rock the lever 53 to a position at which the applied torque on the output shaft is reversed. This brakes the load and as it slows down and approachesl rest, thescrew 64 may be returned toward its rotary Aposition at which the torques of the devices 20--23 are equal when the load comes to rest (if it be an inertia load) or stop short of that position so as to maintain a load holding torque (if it be an overhauling load). thus be applied to brake the load, from high speed all the way to zero speed,- and in fact, if the braking torque thus developed is not removed by return rotation of the screw 64 when the load is braked to rest, it will immediately be reversed under full power and torque, and this latter action which is sometimes wanted corresponds to the action obtained with conventional motor controls and thenknown as plugging the motor.

-No elements additional to those described above for power driven loads are required to provide this improved dynamic braking and plugging action.

Still another type of control may be effected by the hand wheel 16 withv the clutch 11-19 dis- As much torque as desired may 9 engaged. Assuming for simplicity that the load is at the time at rest 'and that the diiierential gear 6d is at rest, upon turning thehand Wheel TS', the differential gear 'it turns and rotates the spider B and the screw B4,

This starts and accelerates the load shaft Il as described; and the differential gear t9 begins to rotate and accelerate. The hand wheel 'l5 may be turned at a sufficiently high speed so as to cause the screw to be turned a number of revolu tions before the differential gear 53 catches up with the differential gear 'it so that the output shaft may be caused to attain a 'desired speed. If now the hand wheel l be released; the screw Gli Will stay in its moved position corresponding to the desired speed of the output shaft-1 and the rotating differential gear 69 will rotate the diierential gear lil, and, throughgears 'NLM Will cause the hand Wheel lt to continue to rotate idly. The output shaft ".vill therefore continue to be driven at its desired speed. A To bring the load to rest, the hand Wheel Viii may be grasped and its rotationstopped. The rotating gear 69 will then rotate the spider i5 and screw St to restore the lever 53 to the posi,- tion at which the output shaft will come to rest. If, instead of merely stopping the hand Wheel Ni,- it be rotated in the opposite direction; the screw 64 will be rotated more rapidly to stop the load more' quickly, or if the hand wheel l5 be turned fast enough and far enough in the said opposite direction, the output shaft will-be stopped by the above described plugging action, as will be understood. l y

Any one of the several controls herein described may be used alone; or any of ythem in combination with another;- the reason for illustrating and describing all of them in one assembly being to simplify the drawing which @therwise would require' numerous additional figures.

While in the preferred embodiment of my invention, utilize a double differential gearing as in Fig. l, and a hydrodynamic torque developing means for applying braldng torques to both gearings to control the speedof the output shaft; the invention may be embodied in another termin which the hydrodynamic torque ydevelopir-ig means is applied to a single differential gearing, and this is illustrated in 4l. A briefer dscription thereof will suffice in View of the foregoing. u A

The differential gearing S6 comprises a ,'spd 8:1 driven by a itor through apirion 85h one differential gear et' is @timecred` to' the output snafu el'; and the otnersifereriuai gear 21 ao the spider si' are connectedrespetiveiy by shafts fll, totwo setsI of discs 2'9-31' of a' """"'ue def v'e'lopirig devicel ZU' which may identical iii/ith the device 2t' of Fig', l.

Ay rocker lever 93', pivoted at 913 and having'a work 6i at one end engaged by a travellingnut 63 on a screw 64 is` engaged at its other end' in ai spool 5d and when rocked on its pivotv changes the thickness of torque transmitting lrns be'A tween the sets of discs 2dy and 31 allas in Fig. l; In this case,Y the pump 38v which supplies oil' to the discs toprovide and maintain the oil films is driven by the motor 88, through gears 95 to 98. When the lever 93 is rocked counter-clockwise, as viewed Fig. 4, until the films between the discs are so thickv that' they transmit no torque, any load connected to the output shaft .fliywill hold ita-t rest. When the fever 33 is rocked clock' Wise, andl reduces the film thickness and' thereby as described develops braking torque on the shaft l0 i8 and diffierential gear 92; the load shaft 9i will be rotated and at a speed commensurable with the' torque and the rocked position of the lever 93;

The lever 93 may be rocked by any of the' means described for Fig. 1 within the area enclosed by the broken line lilo of Fig; l; this area being reproduced in Fig.` 4, and the parts Within'. it being identified as the same as in Fig. 1 by the screw @il and the differential gear t9 and shaft 11|; the shaft li being in this case driven' from the output shaft Si through gears IUILIBZ.- y

Turning the screw t4 in one direction by any of said means `:vill increase the torque applied to the output shaft Si; and its speed; and turni-ng it in the other direction Will decrease the torque and speed; The maximum torque and speed is attained when the discs are moved into actual contact engagement as described for Fig. 1.

'line shaft 9i may therefore be controlled as in the form of Fig. i, but in this case only in one direction ofrotation;

This lapplication is a continuation in part of application Serial yNumberllSZJ filed June 24, 19i4lnovv Patent No; 254645275;

I claim:

1. A power transmission comprising a power output element; a pair of,` differential gea-rings; each gearing comprising three elements; namely, avrotable spider element rotatably supporting a pinion,I and twokrotable gears meshed With the pinion; a first element of each gearing adapted to be continuously driven by motor power; a second element of each gearing being connected to the outputelement by means adapted to apply respective torques oppositely thereto; .the third elements of the gea-rings being continuously driven by the first elements whenl motor driven; restraining means restraining relative rotation of the first and third elements to cause the second elements toapply torques to the output element as aforesaid, and control means to control `the restraining means to'ccntrol the torques applied to the output element and to balance and unbalaiic them, to cause theoutput shaft to have aero Speedwln the applied torqus ai'balanoe'd and to rotate in forward or reverse direction the said appliedA trqus a'r'e correspondingly ubaianceu, and to have a' rotational speed de; teminl by the degree' of applied torque' inb'al'- aos; said restraining yand control means 'coiffprris'ing a pair of relatitelyeotable lements for eachgearing having mutually confronting'faces with a Ispace' therebetweenronef the elements of each pair being' connected tothe corresponding one of the continuously rotating third lements', and the"1 other of the pair connected to' the cr respoiiig one of the elements; means to supply liquid to' the sarei spaces'- r0- maintir a torque-transmitting liquid etui space, ns to increase tri-e thickness* of one sin y to that of other to vary' relativel sinittd toiiqu'es.`

i power taslfi'issio'l o'ollpisil'g' a p'tv'f output element; pair of differential gearings; each` gearing comprising tri-ree elementai namely, a= rotable spider element rotatably supporting a pinion;A and two retable gears mesi-led with the pinion; a iirst element of each-,gearing adapted to be continuously driven by motor povfer and a second elementoi each gearing being. oonn'ectedto the output'element by' meansl adapted to applyrsp'ective t'orqnos oppositel'y' thereto; the third l'# ments of' the' gearings being conunu'ousiy' driven by the first elements whenl motor driven; r'ei straining means restraining relative rotation of the first and third elements to cause the second elements to apply torques to the output element as aforesaid and control means to control the restraining means to control the torques applied to the output element and to balance and unbalance them, to cause the output shaft to have zero speed when the applied torques are balanced and to rotate in forward or reverse direction when the said applied torques are correspondingly unbalanced, and to have a rotational speed determined by the degree of applied torque imbalance; said restraining and control means comprising a pair of relatively-rotable elements for each gearing having mutually confronting faces with a space therebetween, one of the elements of each pair being connected to the corresponding one of the continuously rotating third elements, and the other of the pair connected to the corresponding one of the first elements; means to supply liquid to the said spaces to maintain a torque-transmitting liquid nlm in each space, and means to increase the thickness of one nlm relative to that of the other to vary relatively the transmitted torques, comprising means to adjustably increase the thickness of one film and decrease the thickness of the other, concurrently.

3. A power transmission comprising a power output element; a pair of differential gearings; each gearing comprising three elements, namely, a rotable spider element rotatably supporting a pinion,` and two rotable gears meshed with the pinion; a rst element of each gearing adapted to be continuously driven by motor power; a second element of each gearing being connected to the output element by means adapted to apply respective torques oppositely thereto; the third elements of the gearings being continuously driven by the first elements when motor driven; re-

straining means restraining relative rotation of A the first and third elements to cause the second elements to apply torques to the output element as aforesaid, and control means to control the restraining means to control the torques applied to the output element and to balance and unbalance them, to cause the output shaft to have zero speed when the applied torques are balanced and to rotate in forward or reverse direction when the said applied torques are correspondingly unbalanced, and to have a rotational speed determined by the degree of applied torque imbalance; said restraining and control means comprising a pair of relatively-rotable elements for each gearing having mutually confronting faces with a space therebetween, one of the elements of each pair being connected to the corresponding one of the continuously rotating third elements, and the other of the pair connected to the corresponding one of the first elements; means to supply liquid to the said spaces to maintain a torquetransmitting liquid film in each space, and means to increase the thickness of one film relative to that of the other to vary relatively the transmitted torques, comprising operable means to move one said face toward and from its confronting face; said operable means being operable optionally to entirely close one said space and lockingly engage the corresponding pair of relatively rotatable elements.

4. A power transmission for continuously applying driving torque of variable amount to a load comprising a power output element; a differential gearing comprising three elements namely: a rotable spider element rotatably supporting a pinion, 'and two rotable diiferential gears meshed with the pinion; the spider element adapted to be driven by a continuously running motor; one differential gear connected to the output element; restraining means associated with the other differential gear; comprising a pair of disc-like elements having faces mutually confronting and spaced apart; one disc-like element rotatable by the said other differential gear and the other disc-like element supported so that the one disclike element rotates relative thereto; means for continuously supplying liquid to the space between the disc faces, and continuously maintaining therebetween a liquid film of torque transmitting thickness; and means to adjustably vary the distance between the disc faces, to adjust the torque continuously developed therebetween, to adjustably Vary the torque continuously developed on the said one differential gear.

y5. A power transmission for continuously applying driving torque of variable amount to a load comprising a power output element; a differential gearing comprising three elements namely: a spider element rotatably supporting a pinion, and two differential gears meshed with the pinion; a first gearing element adapted to be driven by a continuously running motor; a second gearing element connected to the output element; restraining means associated with the first and third gearing element; comprising a pair of disc-like elements having faces mutually confronting and spaced apart; one disc-like element rotatably driven by the said third gearing element and the other rotatably driven by the motor driven rst gearing element; means for continuously supplying liquid to the space between the disc faces, and continuously maintaining therebetween a liquid film of torque transmitting thickness; and means to adjustably vary the distance between the disc faces, to adjust the torque continuously developed therebetween, to vary the torque continuously developed on said second gearing element.

6. A power transmission for continuously applying driving torque of variable amount to a load comprising a power output element; a differential gearing comprising three elements namely: a. spider element rotatably supporting a pinion, and two differential gears meshed with the pinion; the spider element adapted to be driven by a continuously running motor; one differential gear connected to the output element; restraining means associated with the other differential gear and the spider element; comprising a pair of disclike elements having faces mutually confronting and spaced apart; one disc-like element rotatable by the said other differential gear; the other disclike element driven by the spider element; means for continuously supplying liquid to the space between the disc faces, and continuously maintaining therebetween a liquid film of torque transmitting thickness; and means to adjustably vary the distance between the disc faces, to adjust the torque continuously developed therebetween, to adjustably vary the torque continuously developed on the said one differential gear.

LEV A. TRO-FIMOV.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 766,314 Yost Aug. 2, 1904 (Other references on following page) Number Number Number Name Date Bear June 14, 1938 Waters Nov. 12, 1940 Jandasek July 25, 1944 FOREIGN PATENTS Country Date Great Britain Dec. 16, 1909 Great Britain Nov. 16, 1933 

